1. Technical Field
The present invention relates in general to an improved apparatus and method of processing workpieces, and in particular to an improved process and apparatus for precision lapping a very small workpiece such as a single magnetoresistive slider.
2. Description of the Related Art
Magnetic recording is employed for large memory capacity requirements in high speed data processing systems. For example, in magnetic disc drive systems, data is read from and written to magnetic recording media utilizing magnetic transducers commonly referred to as magnetic heads. Typically, one or more magnetic recording discs are mounted on a spindle such that the disc can rotate to permit the magnetic head mounted on a moveable arm in position closely adjacent to the disc surface to read or write information thereon.
During operation of the disc drive system, an actuator mechanism moves the magnetic transducer to a desired radial position on the surface of the rotating disc where the head electromagnetically reads or writes data. Usually the head is integrally mounted in a carrier or support referred to as a xe2x80x9cslider.xe2x80x9d A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disc drive system. The slider is aerodynamically shaped to slide over moving air and therefore to maintain a uniform distance from the surface of the rotating disc thereby preventing the head from undesirably contacting the disc.
Typically, a slider is formed with essentially planar areas surrounded by recessed areas etched back from the original surface. The surface of the planar areas that glide over the disc surface during operation is known as the air bearing surface. Large numbers of sliders are fabricated from a single wafer having rows of the magnetic transducers deposited simultaneously on the wafer surface using semiconductor-type process methods. After deposition of the heads is complete, single-row bars are sliced from the wafer, each bar comprising a row of units which can be further processed into sliders having one or more magnetic transducers on their end faces. Each row bar is bonded to a fixture or tool where the bar is processed and then further diced, i.e., separated into sliders having one or more magnetic transducers on their end faces. Each row bar is bonded to a fixture or tool where the bar is processed and then further diced, i.e., separated into individual sliders each slider having at least one magnetic head terminating at the slider air bearing surface.
The slider head is typically an inductive electromagnetic device including magnetic pole pieces which read the data from or write the data onto the recording media surface. In other applications the magnetic head may include a magneto resistive read element for separately reading the recorded data with the inductive heads serving only to write the data. In either application, the various elements terminate on the air bearing surface and function to electromagnetically interact with the data contained on the magnetic recording disc. In order to achieve maximum efficiency from the magnetic heads, the sensing elements must have precision dimensional relationships to each other as well as the application of the slider air bearing surface to the magnetic recording disc. Each head has a polished air bearing surface (ABS) with flatness parameters, such as crown, camber, and twist. The ABS allows the head to xe2x80x9cflyxe2x80x9d above the surface of its respective spinning disk. In order to achieve the desired fly height, fly height variance, take-off speed, and other aerodynamic characteristics, the flatness parameters of the ABS need to be tightly controlled. During manufacturing, it is most critical to grind or lap these elements to very close tolerances of desired thickness in order to achieve the unimpaired functionality required of sliders.
Conventional lapping processes utilize either oscillatory or rotary motion of the workpiece across either a rotating or oscillating lapping plate to provide a random motion of the workpiece over the lapping plate and randomize plate imperfections across the head surface in the course of lapping. During the lapping process, the motion of abrasive particles carried on the surface of the lapping plate is typically along, parallel to, or across the magnetic head elements exposed at the slider air bearing surface. In magnetic head applications, the electrically active components exposed at the air bearing surface are made of relatively softer, ductile materials. These electrically active components during lapping can scratch and smear into the other components causing electrical shorts and degraded head performance. The prior art lapping processes cause different materials exposed at the slider air bearing surface to lap to different depths, resulting in recession or protrusion of the critical head elements relative to the air bearing surface. As a result, poor head performance because of increased space between the critical elements and the recording disc can occur.
Rotating lapping plates having horizontal lapping surfaces in which abrasive particles such as diamond fragments are embedded have been used for lapping and polishing purposes in the high precision lapping of magnetic transducing heads. Generally in these lapping processes, as abrasive slurry utilizing a liquid carrier containing diamond fragments or other abrasive particles is applied to the lapping surface as the lapping plate is rotated relative to the slider or sliders maintained against the lapping surface. Common practice is to periodically refurbish the lapping plate with a lapping abrasion to produce a surface texture suitable for the embedding and retention of the appropriate size of diamond abrasive being used with the lapping process. One of several problems experienced is that the surface is susceptible to rapid change in smoothness as it is used to lap a workpiece during lapping. A change in smoothness effects the hydrodynamic bearing film provided by the liquid component of the abrasive slurry creating a hydroplaning effect which raises the workpiece from the lapping surface to diminish the abrasion action of the particles and substantially increases abrasion time required.
The general idea of interrupting the lapping surface, for example, by forming grooves in the lapping plate is known in the art. Further, material has been used in the troughs so that unspent abrasive liquid is maintained adjacent to the working surface of the lapping plate while spent abrasive fluid is centrifugally removed beyond the lap plate periphery. In other applications, the grooves are formed between working surface areas in which an abrasive such as diamond particles are embedded in a metallic coat.
Problems exist with grooved plates such as excessive width and/or depth of the grooves to allow abrasive particles to lose their effectiveness due to lack of contact with a workpiece. Grooves that are too wide provide surface discontinuity too severe for small work pieces. Forming such grooves is costly and time consuming, even if the grooves can be sized properly. Substantial segments of the lapping surface remain ungrooved, or alternatively a prohibitively large number of grooves are required. Surface uniformity on a micropore scale suitable for lapping smaller pieces has been achieved only with extreme care. In addition, the efficiency of the lapping operation is directly related to the fraction of area at the upper surface since this is the area causing the lapping to occur.
Although a number of processing steps are required to manufacture heads, the ABS flatness parameters are primarily determined during the final lapping process. The final lapping process may be performed on the heads after they have been separated or segmented into individual pieces, or on rows of heads prior to the segmentation step. This process requires the head or row to be restrained while an abrasive plate of specified curvature is rubbed against it. As the plate abrades the surface of the head, the abrasion process causes material removal on the head ABS and, in the optimum case, will cause the ABS to conform to the contour or curvature of the plate. The final lapping process also creates and defines the proper magnetic read sensor and write element material heights needed for magnetic recording.
There are a number of factors that affect the accuracy of ABS curvature during the final lapping process. These include diamond size/morphology, lubricant chemistry, lapping surface velocity, plate material, lapping motion/path on the plate, and other lapping parameters. In addition to these parameters, three critical conditions must be satisfied. First, it is essential that the contour of the abrasive plate be tightly controlled since, in the best case, the ABS will conform to the curvature of the plate. In addition, all components of the process, including the head/row, must be restrained without distortion during lapping. Any variance in the restraining forces will cause the parts to distort and/or elastically deform upon removal of the forces. For example, if a head or row is lapped on an absolutely flat surface while it is clamped in a fixture, the part will elastically deform to a non-flat condition when it is released. The amount of deformation is proportional to the amount of elastic distortion created when the part was initially clamped.
The single slider lapping process (SSP) is a recent approach to improve the dimensional control of one of the key parameters for the magnetoresistive sensor in disk drives. In this process the individual slider is placed in a fixture and lapped until the desired resistance target is achieved. The slider is gripped on two ends, one of which has the electrical contacts pads which allow sensing of the desired resistance. It is necessary to apply sufficient force to the slider to maintain its position during lapping and to make electrical contact to the pads.
There is a countering factor opposing the application of large gripping force which is the need to avoid distorting the slider during gripping (whose relaxed state after lapping would retain the opposite distortion.) So there is a rationale to decrease the gripping force to the minimum. The distortion-causing load limit will be decreased by about 3xc3x97 as a progression is made to femto sliders, and further reduction if a progression is made to a softer substrate material in the future (assuming crown/camber targets do not get tighter). Consequently, there will be an ever increasing emphasis on lower gripping forces as the SSP progresses. Thus, an improved apparatus and method for accurately defining the curvature of an ABS during the final lapping process is needed.
One embodiment of the present invention photolithographically defines patterns on a lapping plate which are electroplated to produce lands with well-defined channels. By choosing a particular geometry, the retention force is significantly reduced over prior art options, while still retaining a high land area fraction. The material may be electroplated onto sufficiently thin substrates to allow conformation to a curved vacuum chuck. Before electroplating resist is applied and patterned, an exposed pattern is left in the underlying metallization seed layer on both sides. A plasma cleaning step is used to clean the resist residue from the bottom of the holes, the plates are electroplated, and then the remaining resist is removed.
In one particular embodiment, the lapping plate is formed from a glass substrate, Crxe2x80x94Cu sputtered, and has spun resist. Both sides of the substrate are patterned and plated (i.e., two lapping surfaces per substrate). The plate has 25 xcexcm square lands with 10 xcexcm spaces between lands, and has a 5 to 30 xcexcm plating of Snxe2x80x94Bi. The plate is press flattened or turned on both sides, and one of the lapping surfaces is initially resist-protected until it is used, which also isolates the plate electrically. The small land and space configuration gives rise to reduced hydrodynamic forces between the plate and workpiece as the workpiece is removed from the plate.
Another favorable aspect of the present invention is the reduced thickness of the substrate used for the lapping plate. It is desirable to use a vacuum chuck capable of pulling a thin, flat lapping plate against it to define the curvature. This allows the lapping plate to be charged with abrasive by a flat charging ring.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.